PERLEMBED(1)
NNAAMMEE
perlembed - how to embed perl in your C program
DDEESSCCRRIIPPTTIIOONN
PPRREEAAMMBBLLEE
Do you want to:
UUssee CC ffrroomm PPeerrll??
Read the perlcall manpage and the perlxs manpage.
UUssee aa UUnniixx pprrooggrraamm ffrroomm PPeerrll??
Read about back-quotes and about system and exec in
the perlfunc manpage.
UUssee PPeerrll ffrroomm PPeerrll??
Read about the do entry in the perlfunc manpage and
the eval entry in the perlfunc manpage and the
require entry in the perlfunc manpage and the use
entry in the perlfunc manpage.
UUssee CC ffrroomm CC??
Rethink your design.
UUssee PPeerrll ffrroomm CC??
Read on...
RROOAADDMMAAPP
the section on Compiling your C program
There's one example in each of the nine sections:
the section on Adding a Perl interpreter to your C program
the section on Calling a Perl subroutine from your C
program
the section on Evaluating a Perl statement from your C
program
the section on Performing Perl pattern matches and
substitutions from your C program
the section on Fiddling with the Perl stack from your C
program
the section on Maintaining a persistent interpreter
the section on Maintaining multiple interpreter instances
the section on Using Perl modules, which themselves use C
libraries, from your C program
the section on Embedding Perl under Win32
CCoommppiilliinngg yyoouurr CC pprrooggrraamm
If you have trouble compiling the scripts in this
documentation, you're not alone. The cardinal rule:
COMPILE THE PROGRAMS IN EXACTLY THE SAME WAY THAT YOUR
PERL WAS COMPILED. (Sorry for yelling.)
Also, every C program that uses Perl must link in the perl
library. What's that, you ask? Perl is itself written in
C; the perl library is the collection of compiled C
programs that were used to create your perl executable
(/usr/bin/perl or equivalent). (Corollary: you can't use
Perl from your C program unless Perl has been compiled on
your machine, or installed properly--that's why you
shouldn't blithely copy Perl executables from machine to
machine without also copying the lib directory.)
When you use Perl from C, your C program
will--usually--allocate, "run", and deallocate a
PerlInterpreter object, which is defined by the perl
library.
If your copy of Perl is recent enough to contain this
documentation (version 5.002 or later), then the perl
library (and EXTERN.h and perl.h, which you'll also need)
will reside in a directory that looks like this:
/usr/local/lib/perl5/your_architecture_here/CORE
or perhaps just
/usr/local/lib/perl5/CORE
or maybe something like
/usr/opt/perl5/CORE
Execute this statement for a hint about where to find
CORE:
perl -MConfig -e 'print $Config{archlib}'
Here's how you'd compile the example in the next section,
the section on Adding a Perl interpreter to your C
program, on my Linux box:
% gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
-I/usr/local/lib/perl5/i586-linux/5.003/CORE
-L/usr/local/lib/perl5/i586-linux/5.003/CORE
-o interp interp.c -lperl -lm
(That's all one line.) On my DEC Alpha running 5.003_05,
the incantation is a bit different:
% cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
-I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
-L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
-D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
How can you figure out what to add? Assuming your Perl is
post-5.001, execute a perl -V command and pay special
attention to the "cc" and "ccflags" information.
You'll have to choose the appropriate compiler (cc, gcc,
et al.) for your machine: perl -MConfig -e 'print
$Config{cc}' will tell you what to use.
You'll also have to choose the appropriate library
directory (/usr/local/lib/...) for your machine. If your
compiler complains that certain functions are undefined,
or that it can't locate -lperl, then you need to change
the path following the -L. If it complains that it can't
find EXTERN.h and perl.h, you need to change the path
following the -I.
You may have to add extra libraries as well. Which ones?
Perhaps those printed by
perl -MConfig -e 'print $Config{libs}'
Provided your perl binary was properly configured and
installed the EExxttUUttiillss::::EEmmbbeedd module will determine all of
this information for you:
% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
If the EExxttUUttiillss::::EEmmbbeedd module isn't part of your Perl
distribution, you can retrieve it from
http://www.perl.com/perl/CPAN/modules/by-
module/ExtUtils::Embed. (If this documentation came from
your Perl distribution, then you're running 5.004 or
better and you already have it.)
The EExxttUUttiillss::::EEmmbbeedd kit on CPAN also contains all source
code for the examples in this document, tests, additional
examples and other information you may find useful.
AAddddiinngg aa PPeerrll iinntteerrpprreetteerr ttoo yyoouurr CC pprrooggrraamm
In a sense, perl (the C program) is a good example of
embedding Perl (the language), so I'll demonstrate
embedding with miniperlmain.c, from the source
distribution. Here's a bastardized, nonportable version
of miniperlmain.c containing the essentials of embedding:
#include <EXTERN.h> /* from the Perl distribution */
#include <perl.h> /* from the Perl distribution */
static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
int main(int argc, char **argv, char **env)
{
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
perl_run(my_perl);
perl_destruct(my_perl);
perl_free(my_perl);
}
Notice that we don't use the env pointer. Normally handed
to perl_parse as its final argument, env here is replaced
by NULL, which means that the current environment will be
used.
Now compile this program (I'll call it interp.c) into an
executable:
% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
After a successful compilation, you'll be able to use
interp just like perl itself:
% interp
print "Pretty Good Perl \n";
print "10890 - 9801 is ", 10890 - 9801;
<CTRL-D>
Pretty Good Perl
10890 - 9801 is 1089
or
% interp -e 'printf("%x", 3735928559)'
deadbeef
You can also read and execute Perl statements from a file
while in the midst of your C program, by placing the
filename in argv[1] before calling perl_run().
CCaalllliinngg aa PPeerrll ssuubbrroouuttiinnee ffrroomm yyoouurr CC pprrooggrraamm
To call individual Perl subroutines, you can use any of
the ppeerrll__ccaallll__** functions documented in the the perlcall
manpage manpage. In this example we'll use
perl_call_argv.
That's shown below, in a program I'll call showtime.c.
#include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *args[] = { NULL };
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, argc, argv, NULL);
/*** skipping perl_run() ***/
perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
perl_destruct(my_perl);
perl_free(my_perl);
}
where showtime is a Perl subroutine that takes no
arguments (that's the G_NOARGS) and for which I'll ignore
the return value (that's the G_DISCARD). Those flags, and
others, are discussed in the perlcall manpage.
I'll define the showtime subroutine in a file called
showtime.pl:
print "I shan't be printed.";
sub showtime {
print time;
}
Simple enough. Now compile and run:
% cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% showtime showtime.pl
818284590
yielding the number of seconds that elapsed between
January 1, 1970 (the beginning of the Unix epoch), and the
moment I began writing this sentence.
In this particular case we don't have to call perl_run,
but in general it's considered good practice to ensure
proper initialization of library code, including execution
of all object DESTROY methods and package END {} blocks.
If you want to pass arguments to the Perl subroutine, you
can add strings to the NULL-terminated args list passed to
perl_call_argv. For other data types, or to examine
return values, you'll need to manipulate the Perl stack.
That's demonstrated in the last section of this document:
the section on Fiddling with the Perl stack from your C
program.
EEvvaalluuaattiinngg aa PPeerrll ssttaatteemmeenntt ffrroomm yyoouurr CC pprrooggrraamm
Perl provides two API functions to evaluate pieces of Perl
code. These are the perl_eval_sv() entry in the perlguts
manpage and the perl_eval_pv() entry in the perlguts
manpage.
Arguably, these are the only routines you'll ever need to
execute snippets of Perl code from within your C program.
Your code can be as long as you wish; it can contain
multiple statements; it can employ the use entry in the
perlfunc manpage, the require entry in the perlfunc
manpage and the do entry in the perlfunc manpage to
include external Perl files.
perl_eval_pv() lets us evaluate individual Perl strings,
and then extract variables for coercion into C types. The
following program, string.c, executes three Perl strings,
extracting an int from the first, a float from the second,
and a char * from the third.
#include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
main (int argc, char **argv, char **env)
{
char *embedding[] = { "", "-e", "0" };
my_perl = perl_alloc();
perl_construct( my_perl );
perl_parse(my_perl, NULL, 3, embedding, NULL);
perl_run(my_perl);
/** Treat $a as an integer **/
perl_eval_pv("$a = 3; $a **= 2", TRUE);
printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
/** Treat $a as a float **/
perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
/** Treat $a as a string **/
perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));
perl_destruct(my_perl);
perl_free(my_perl);
}
All of those strange functions with sv in their names help
convert Perl scalars to C types. They're described in the
perlguts manpage.
If you compile and run string.c, you'll see the results of
using SvIV() to create an int, SvNV() to create a float,
and SvPV() to create a string:
a = 9
a = 9.859600
a = Just Another Perl Hacker
In the example above, we've created a global variable to
temporarily store the computed value of our eval'd
expression. It is also possible and in most cases a
better strategy to fetch the return value from the
perl_eval_pv manpage instead. Example:
...
SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
printf("%s\n", SvPV(val,na));
...
This way, we avoid namespace pollution by not creating
global variables and we've simplified our code as well.
PPeerrffoorrmmiinngg PPeerrll ppaatttteerrnn mmaattcchheess aanndd ssuubbssttiittuuttiioonnss ffrroomm
yyoouurr CC pprrooggrraamm
The perl_eval_sv() function lets us evaluate chunks of
Perl code, so we can define some functions that use it to
"specialize" in matches and substitutions: match(),
substitute(), and matches().
char match(SV *string, char *pattern);
Given a string and a pattern (e.g., m/clasp/ or /\b\w*\b/,
which in your C program might appear as "/\\b\\w*\\b/"),
match() returns 1 if the string matches the pattern and 0
otherwise.
int substitute(SV **string, char *pattern);
Given a pointer to an SV and an =~ operation (e.g.,
s/bob/robert/g or tr[A-Z][a-z]), substitute() modifies the
string within the AV at according to the operation,
returning the number of substitutions made.
int matches(SV *string, char *pattern, AV **matches);
Given an SV, a pattern, and a pointer to an empty AV,
matches() evaluates $string =~ $pattern in an array
context, and fills in matches with the array elements,
returning the number of matches found.
Here's a sample program, match.c, that uses all three
(long lines have been wrapped here):
#include <EXTERN.h>
#include <perl.h>
/** my_perl_eval_sv(code, error_check)
** kinda like perl_eval_sv(),
** but we pop the return value off the stack
**/
SV* my_perl_eval_sv(SV *sv, I32 croak_on_error)
{
dSP;
SV* retval;
PUSHMARK(sp);
perl_eval_sv(sv, G_SCALAR);
SPAGAIN;
retval = POPs;
PUTBACK;
if (croak_on_error && SvTRUE(GvSV(errgv)))
croak(SvPVx(GvSV(errgv), na));
return retval;
}
/** match(string, pattern)
**
** Used for matches in a scalar context.
**
** Returns 1 if the match was successful; 0 otherwise.
**/
I32 match(SV *string, char *pattern)
{
SV *command = newSV(0), *retval;
sv_setpvf(command, "my $string = '%s'; $string =~ %s",
SvPV(string,na), pattern);
retval = my_perl_eval_sv(command, TRUE);
SvREFCNT_dec(command);
return SvIV(retval);
}
/** substitute(string, pattern)
**
** Used for =~ operations that modify their left-hand side (s/// and tr///)
**
** Returns the number of successful matches, and
** modifies the input string if there were any.
**/
I32 substitute(SV **string, char *pattern)
{
SV *command = newSV(0), *retval;
sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
SvPV(*string,na), pattern);
retval = my_perl_eval_sv(command, TRUE);
SvREFCNT_dec(command);
*string = perl_get_sv("string", FALSE);
return SvIV(retval);
}
/** matches(string, pattern, matches)
**
** Used for matches in an array context.
**
** Returns the number of matches,
** and fills in **matches with the matching substrings
**/
I32 matches(SV *string, char *pattern, AV **match_list)
{
SV *command = newSV(0);
I32 num_matches;
sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
SvPV(string,na), pattern);
my_perl_eval_sv(command, TRUE);
SvREFCNT_dec(command);
*match_list = perl_get_av("array", FALSE);
num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/
return num_matches;
}
main (int argc, char **argv, char **env)
{
PerlInterpreter *my_perl = perl_alloc();
char *embedding[] = { "", "-e", "0" };
AV *match_list;
I32 num_matches, i;
SV *text = newSV(0);
perl_construct(my_perl);
perl_parse(my_perl, NULL, 3, embedding, NULL);
sv_setpv(text, "When he is at a convenience store and the bill comes to some amount like 76 cents, Maynard is aware that there is something he *should* do, something that will enable him to get back a quarter, but he has no idea *what*. He fumbles through his red squeezey changepurse and gives the boy three extra pennies with his dollar, hoping that he might luck into the correct amount. The boy gives him back two of his own pennies and then the big shiny quarter that is his prize. -RICHH");
if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
printf("match: Text contains the word 'quarter'.\n\n");
else
printf("match: Text doesn't contain the word 'quarter'.\n\n");
if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
printf("match: Text contains the word 'eighth'.\n\n");
else
printf("match: Text doesn't contain the word 'eighth'.\n\n");
/** Match all occurrences of /wi../ **/
num_matches = matches(text, "m/(wi..)/g", &match_list);
printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
for (i = 0; i < num_matches; i++)
printf("match: %s\n", SvPV(*av_fetch(match_list, i, FALSE),na));
printf("\n");
/** Remove all vowels from text **/
num_matches = substitute(&text, "s/[aeiou]//gi");
if (num_matches) {
printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
num_matches);
printf("Now text is: %s\n\n", SvPV(text,na));
}
/** Attempt a substitution **/
if (!substitute(&text, "s/Perl/C/")) {
printf("substitute: s/Perl/C...No substitution made.\n\n");
}
SvREFCNT_dec(text);
perl_destruct_level = 1;
perl_destruct(my_perl);
perl_free(my_perl);
}
which produces the output (again, long lines have been
wrapped here)
match: Text contains the word 'quarter'.
match: Text doesn't contain the word 'eighth'.
matches: m/(wi..)/g found 2 matches...
match: will
match: with
substitute: s/[aeiou]//gi...139 substitutions made.
Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
substitute: s/Perl/C...No substitution made.
FFiiddddlliinngg wwiitthh tthhee PPeerrll ssttaacckk ffrroomm yyoouurr CC pprrooggrraamm
When trying to explain stacks, most computer science
textbooks mumble something about spring-loaded columns of
cafeteria plates: the last thing you pushed on the stack
is the first thing you pop off. That'll do for our
purposes: your C program will push some arguments onto
"the Perl stack", shut its eyes while some magic happens,
and then pop the results--the return value of your Perl
subroutine--off the stack.
First you'll need to know how to convert between C types
and Perl types, with newSViv() and sv_setnv() and newAV()
and all their friends. They're described in the perlguts
manpage.
Then you'll need to know how to manipulate the Perl stack.
That's described in the perlcall manpage.
Once you've understood those, embedding Perl in C is easy.
Because C has no builtin function for integer
exponentiation, let's make Perl's ** operator available to
it (this is less useful than it sounds, because Perl
implements ** with C's pow() function). First I'll create
a stub exponentiation function in power.pl:
sub expo {
my ($a, $b) = @_;
return $a ** $b;
}
Now I'll create a C program, power.c, with a function
PerlPower() that contains all the perlguts necessary to
push the two arguments into expo() and to pop the return
value out. Take a deep breath...
#include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
static void
PerlPower(int a, int b)
{
dSP; /* initialize stack pointer */
ENTER; /* everything created after here */
SAVETMPS; /* ...is a temporary variable. */
PUSHMARK(sp); /* remember the stack pointer */
XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
PUTBACK; /* make local stack pointer global */
perl_call_pv("expo", G_SCALAR); /* call the function */
SPAGAIN; /* refresh stack pointer */
/* pop the return value from stack */
printf ("%d to the %dth power is %d.\n", a, b, POPi);
PUTBACK;
FREETMPS; /* free that return value */
LEAVE; /* ...and the XPUSHed "mortal" args.*/
}
int main (int argc, char **argv, char **env)
{
char *my_argv[] = { "", "power.pl" };
my_perl = perl_alloc();
perl_construct( my_perl );
perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
perl_run(my_perl);
PerlPower(3, 4); /*** Compute 3 ** 4 ***/
perl_destruct(my_perl);
perl_free(my_perl);
}
Compile and run:
% cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% power
3 to the 4th power is 81.
MMaaiinnttaaiinniinngg aa ppeerrssiisstteenntt iinntteerrpprreetteerr
When developing interactive and/or potentially long-
running applications, it's a good idea to maintain a
persistent interpreter rather than allocating and
constructing a new interpreter multiple times. The major
reason is speed: since Perl will only be loaded into
memory once.
However, you have to be more cautious with namespace and
variable scoping when using a persistent interpreter. In
previous examples we've been using global variables in the
default package main. We knew exactly what code would be
run, and assumed we could avoid variable collisions and
outrageous symbol table growth.
Let's say your application is a server that will
occasionally run Perl code from some arbitrary file. Your
server has no way of knowing what code it's going to run.
Very dangerous.
If the file is pulled in by perl_parse(), compiled into a
newly constructed interpreter, and subsequently cleaned
out with perl_destruct() afterwards, you're shielded from
most namespace troubles.
One way to avoid namespace collisions in this scenario is
to translate the filename into a guaranteed-unique package
name, and then compile the code into that package using
the eval entry in the perlfunc manpage. In the example
below, each file will only be compiled once. Or, the
application might choose to clean out the symbol table
associated with the file after it's no longer needed.
Using the perl_call_argv entry in the perlcall manpage,
We'll call the subroutine Embed::Persistent::eval_file
which lives in the file persistent.pl and pass the
filename and boolean cleanup/cache flag as arguments.
Note that the process will continue to grow for each file
that it uses. In addition, there might be AUTOLOADed
subroutines and other conditions that cause Perl's symbol
table to grow. You might want to add some logic that
keeps track of the process size, or restarts itself after
a certain number of requests, to ensure that memory
consumption is minimized. You'll also want to scope your
variables with the my entry in the perlfunc manpage
whenever possible.
package Embed::Persistent;
#persistent.pl
use strict;
use vars '%Cache';
sub valid_package_name {
my($string) = @_;
$string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
# second pass only for words starting with a digit
$string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
# Dress it up as a real package name
$string =~ s|/|::|g;
return "Embed" . $string;
}
#borrowed from Safe.pm
sub delete_package {
my $pkg = shift;
my ($stem, $leaf);
no strict 'refs';
$pkg = "main::$pkg\::"; # expand to full symbol table name
($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
my $stem_symtab = *{$stem}{HASH};
delete $stem_symtab->{$leaf};
}
sub eval_file {
my($filename, $delete) = @_;
my $package = valid_package_name($filename);
my $mtime = -M $filename;
if(defined $Cache{$package}{mtime}
&&
$Cache{$package}{mtime} <= $mtime)
{
# we have compiled this subroutine already,
# it has not been updated on disk, nothing left to do
print STDERR "already compiled $package->handler\n";
}
else {
local *FH;
open FH, $filename or die "open '$filename' $!";
local($/) = undef;
my $sub = <FH>;
close FH;
#wrap the code into a subroutine inside our unique package
my $eval = qq{package $package; sub handler { $sub; }};
{
# hide our variables within this block
my($filename,$mtime,$package,$sub);
eval $eval;
}
die $@ if $@;
#cache it unless we're cleaning out each time
$Cache{$package}{mtime} = $mtime unless $delete;
}
eval {$package->handler;};
die $@ if $@;
delete_package($package) if $delete;
#take a look if you want
#print Devel::Symdump->rnew($package)->as_string, $/;
}
1;
__END__
/* persistent.c */
#include <EXTERN.h>
#include <perl.h>
/* 1 = clean out filename's symbol table after each request, 0 = don't */
#ifndef DO_CLEAN
#define DO_CLEAN 0
#endif
static PerlInterpreter *perl = NULL;
int
main(int argc, char **argv, char **env)
{
char *embedding[] = { "", "persistent.pl" };
char *args[] = { "", DO_CLEAN, NULL };
char filename [1024];
int exitstatus = 0;
if((perl = perl_alloc()) == NULL) {
fprintf(stderr, "no memory!");
exit(1);
}
perl_construct(perl);
exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
if(!exitstatus) {
exitstatus = perl_run(perl);
while(printf("Enter file name: ") && gets(filename)) {
/* call the subroutine, passing it the filename as an argument */
args[0] = filename;
perl_call_argv("Embed::Persistent::eval_file",
G_DISCARD | G_EVAL, args);
/* check $@ */
if(SvTRUE(GvSV(errgv)))
fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
}
}
perl_destruct_level = 0;
perl_destruct(perl);
perl_free(perl);
exit(exitstatus);
}
Now compile:
% cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Here's a example script file:
#test.pl
my $string = "hello";
foo($string);
sub foo {
print "foo says: @_\n";
}
Now run:
% persistent
Enter file name: test.pl
foo says: hello
Enter file name: test.pl
already compiled Embed::test_2epl->handler
foo says: hello
Enter file name: ^C
MMaaiinnttaaiinniinngg mmuullttiippllee iinntteerrpprreetteerr iinnssttaanncceess
Some rare applications will need to create more than one
interpreter during a session. Such an application might
sporadically decide to release any resources associated
with the interpreter.
The program must take care to ensure that this takes place
before the next interpreter is constructed. By default,
the global variable perl_destruct_level is set to 0, since
extra cleaning isn't needed when a program has only one
interpreter.
Setting perl_destruct_level to 1 makes everything squeaky
clean:
perl_destruct_level = 1;
while(1) {
...
/* reset global variables here with perl_destruct_level = 1 */
perl_construct(my_perl);
...
/* clean and reset _everything_ during perl_destruct */
perl_destruct(my_perl);
perl_free(my_perl);
...
/* let's go do it again! */
}
When perl_destruct() is called, the interpreter's syntax
parse tree and symbol tables are cleaned up, and global
variables are reset.
Now suppose we have more than one interpreter instance
running at the same time. This is feasible, but only if
you used the -DMULTIPLICITY flag when building Perl. By
default, that sets perl_destruct_level to 1.
Let's give it a try:
#include <EXTERN.h>
#include <perl.h>
/* we're going to embed two interpreters */
/* we're going to embed two interpreters */
#define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
int main(int argc, char **argv, char **env)
{
PerlInterpreter
*one_perl = perl_alloc(),
*two_perl = perl_alloc();
char *one_args[] = { "one_perl", SAY_HELLO };
char *two_args[] = { "two_perl", SAY_HELLO };
perl_construct(one_perl);
perl_construct(two_perl);
perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
perl_run(one_perl);
perl_run(two_perl);
perl_destruct(one_perl);
perl_destruct(two_perl);
perl_free(one_perl);
perl_free(two_perl);
}
Compile as usual:
% cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Run it, Run it:
% multiplicity
Hi, I'm one_perl
Hi, I'm two_perl
UUssiinngg PPeerrll mmoodduulleess,, wwhhiicchh tthheemmsseellvveess uussee CC lliibbrraarriieess,, ffrroomm
yyoouurr CC pprrooggrraamm
If you've played with the examples above and tried to
embed a script that use()s a Perl module (such as Socket)
which itself uses a C or C++ library, this probably
happened:
Can't load module Socket, dynamic loading not available in this perl.
(You may need to build a new perl executable which either supports
dynamic loading or has the Socket module statically linked into it.)
What's wrong?
Your interpreter doesn't know how to communicate with
these extensions on its own. A little glue will help. Up
until now you've been calling perl_parse(), handing it
NULL for the second argument:
perl_parse(my_perl, NULL, argc, my_argv, NULL);
That's where the glue code can be inserted to create the
initial contact between Perl and linked C/C++ routines.
Let's take a look some pieces of perlmain.c to see how
Perl does this:
#ifdef __cplusplus
# define EXTERN_C extern "C"
#else
# define EXTERN_C extern
#endif
static void xs_init _((void));
EXTERN_C void boot_DynaLoader _((CV* cv));
EXTERN_C void boot_Socket _((CV* cv));
EXTERN_C void
xs_init()
{
char *file = __FILE__;
/* DynaLoader is a special case */
newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
newXS("Socket::bootstrap", boot_Socket, file);
}
Simply put: for each extension linked with your Perl
executable (determined during its initial configuration on
your computer or when adding a new extension), a Perl
subroutine is created to incorporate the extension's
routines. Normally, that subroutine is named
Module::bootstrap() and is invoked when you say use
Module. In turn, this hooks into an XSUB, boot_Module,
which creates a Perl counterpart for each of the
extension's XSUBs. Don't worry about this part; leave
that to the xsubpp and extension authors. If your
extension is dynamically loaded, DynaLoader creates
Module::bootstrap() for you on the fly. In fact, if you
have a working DynaLoader then there is rarely any need to
link in any other extensions statically.
Once you have this code, slap it into the second argument
of perl_parse():
perl_parse(my_perl, xs_init, argc, my_argv, NULL);
Then compile:
% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% interp
use Socket;
use SomeDynamicallyLoadedModule;
print "Now I can use extensions!\n"'
EExxttUUttiillss::::EEmmbbeedd can also automate writing the xs_init glue
code.
% perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
% cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
% cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
% cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
Consult the perlxs manpage and the perlguts manpage for
more details.
EEmmbbeeddddiinngg PPeerrll uunnddeerr WWiinn3322
At the time of this writing, there are two versions of
Perl which run under Win32. Interfacing to Activeware's
Perl library is quite different from the examples in this
documentation, as significant changes were made to the
internal Perl API. However, it is possible to embed
Activeware's Perl runtime, see the Perl for Win32 FAQ:
http://www.perl.com/perl/faq/win32/Perl_for_Win32_FAQ.html
With the "official" Perl version 5.004 or higher, all the
examples within this documentation will compile and run
untouched, although, the build process is slightly
different between Unix and Win32.
For starters, backticks don't work under the Win32 native
command shell! The ExtUtils::Embed kit on CPAN ships with
a script called ggeennmmaakkee, which generates a simple makefile
to build a program from a single C source file. It can be
used like so:
C:\ExtUtils-Embed\eg> perl genmake interp.c
C:\ExtUtils-Embed\eg> nmake
C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"
You may wish to use a more robust environment such as the
MS Developer stdio. In this case, to generate perlxsi.c
run:
perl -MExtUtils::Embed -e xsinit
Create a new project, Insert -> Files into Project:
perlxsi.c, perl.lib, and your own source files, e.g.
interp.c. Typically you'll find perl.lib in
CC::\\ppeerrll\\lliibb\\CCOORREE, if not, you should see the CCOORREE
directory relative to perl -V:archlib. The studio will
also need this path so it knows where to find Perl include
files. This path can be added via the Tools -> Options ->
Directories menu. Finnally, select Build -> Build
interp.exe and you're ready to go!
MMOORRAALL
You can sometimes write faster code in C, but you can
always write code faster in Perl. Because you can use
each from the other, combine them as you wish.
AAUUTTHHOORR
Jon Orwant and lt;orwant@tpj.com and Doug MacEachern
lt;dougm@osf.org, with small contributions from Tim Bunce,
Tom Christiansen, Hallvard Furuseth, Dov Grobgeld, and
Ilya Zakharevich.
Check out Doug's article on embedding in Volume 1, Issue 4
of The Perl Journal. Info about TPJ is available from
http://tpj.com.
July 17, 1997
Some of this material is excerpted from Jon Orwant's book:
Perl 5 Interactive, Waite Group Press, 1996 (ISBN
1-57169-064-6) and appears courtesy of Waite Group Press.
CCOOPPYYRRIIGGHHTT
Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon
Orwant. All Rights Reserved.
Although destined for release with the standard Perl
distribution, this document is not public domain, nor is
any of Perl and its documentation. Permission is granted
to freely distribute verbatim copies of this document
provided that no modifications outside of formatting be
made, and that this notice remain intact. You are
permitted and encouraged to use its code and derivatives
thereof in your own source code for fun or for profit as
you see fit.